James J. Shieh

Rheology and microstructure of low-fat Mozzarella cheese

The contributions of fat and moisture content to Mozzarella cheese texture were investigated to provide a basis for developing low-fat cheese with consumer acceptability. The characteristics of low-fat high-moisture (LFHM) experimental Mozzarella cheeses before and after 6 weeks of refrigerated storage were compared with those of high-fat low-moisture controls. High levels of either moisture in nonfat substance or fat in dry matter (FDM) were accompanied by decreases in hardness, complex viscosity, and elastic modulus and increases in meltability during the storage time. Starter culture bacteria were observed at the surface of the fat droplets, the latter having a tendency to coalesce during storage. Development of texture and meltability in LFHM Mozzarella appeared to be directly related to increased proteolysis of αs1-casein observed during storage. These results show the feasibility of making Mozzarella cheese containing <25% FDM with textural properties similar to those of a full-fat cheese if the product contains enough moisture and is stored under refrigeration for several weeks.

Rheology of Reduced-Fat Mozzarella Cheese

Reduction of dietary fat by Americans has led to the introduction of various low-fat dairy products. Consumption of Mozzarella cheese in the U.S. has reached 3.5 kg per person per year (USDA, 1993), making this variety an appropriate target for fat reduction. Our laboratory has developed a “light” Mozzarella containing <10% fat (Tunick et al., 1991, 1993a, 1993b) which is currently being tested for use in the National School Lunch Program. The effects of cooking temperature, moisture level, and storage time were examined to determine which combination produces the best product. Meltability studies were of particular interest since three-fourths of the Mozzarella cheese produced in the U.S. is used in pizza (Kindstedt, 1993). Homogenization of cheesemilk was also investigated as a possible means of enhancing textural properties and because homogenization is required when recombined milks are used for cheesemaking. In this study, texture profile analysis, small amplitude dynamic oscillatory shear measurements, and meltability measurements were used to compare the rheological properties of low-fat and full-fat Mozzarella cheeses.

ESR evidence for sequential divalent cation binding in higher plant cell walls

Abstract Electron spin resonance linewidth measurements have been made on intact cell walls exchanged with various combinations of Mn2+ and Ca2+. These experiments were performed to find the Mn2+ nearest-neighbor distance and thereby determine whether carboxylate-Mn2+ complexes potentiate ion association at adjacent sites on cell wall polyuronides. Our results show that as the fraction of available binding sites occupied by Mn2+ increased from 2% to 27%, the nearest-neighbor distance parameter decreased only from 14 to 11 A. These distances are close to polyuronide interanionic spacings. The small change in the distance parameter with concentration is evidence for sequential rather than random binding. Competitive ion-exchange with Ca2+ was found to reduce the Mn2+ spin-spin line broadening at similar total bound Mn2+ concentrations. This is expected only if Ca2+ competes at adjacent sites. The data presented offer strong support for the hypothesis that carboxylate groups near already occupied sites have a greater affinity for divalent cations than other sites along the polyuronide main chain.

Interaction of radiation-generated free radicals with collagen and metalloproteins using cesium-137 gamma source

Abstract The interaction of collagen and metalloproteins with radiation-generated radicals has been studied using spectrophotometric, chromatographic, and ESR techniques. The hydroxyl radical (·OH) reacted with and caused polymerization of acid soluble collagen. Similar reactions were also observed in a ferrimyoglobin and cytochrome C system. Insoluble collagen from bovine muscle subjected to radiation is followed by a first-order process for the decay of free radicals, depending on relative humidity of the system. When the samples were irradiated with 3 kGy at 25°C by a Cesium-137 Irradiator, the observed half life (hr) of free radicals in the samples decreased with increase of relative humidity RH: 31% > 69% > 100%. When collagen, previously kept dry or under 31% RH, was irradiated with 3 kGy at 77°K (-196°C), the decay of free radicals reached a plateau with annealing at -120°C or higher. The decay kept decreasing with annealing at -100°C or higher temperature when collagen maintained at 69 and 100% RH was used. It is concluded that the free radicals in moistened collagen from bovine muscle decreased at a higher rate than in dried collagen. This suggests that free radicals may persist for a longer period of time in irradiated dry proteins of food or animal feed than in foods of higher moisture extent.